1 mole of NH3 = 1 N + 3 H = 4 atoms
= 4 × 6.023 × 1023 atoms and occupies 22.4 lit at s.t.p.
22.4 lit of NH3 has 4 × 6.023 × 1023 atoms
⇒ 10 lit will have = 4 × 6.023 × 10^{23}\over22.4 × 10
= 40\over22.4 × 6.023 × 1023
= 1.786 × 6.023 × 1023
Hence, number of atoms in 10 litres of ammonia = 1.786 × 6.023 × 1023 atoms